Accuracy of fetal gender determination in the first trimester using three‐dimensional ultrasound

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Abstract
Objectives To evaluate the accuracy of three‐dimensional (3D) ultrasound in fetal gender assignment in the first trimester. Methods A series of pregnant women attending at 11 to 13 + 6 weeks for the nuchal translucency (NT) scan were enrolled into the study. An ultrasound volume of each fetus was obtained and stored for offline analysis. On the reconstructed mid‐sagittal plane, the angle between the genital tubercle and an imaginary line passing tangentially through the fetal back (genital angle) was estimated and a receiver–operating characteristics (ROC) curve was constructed to determine the best cut‐off for genital angle in fetal male gender determination. Fetal gender was subsequently ascertained in all cases. To calculate the interobserver variability, a second operator repeated the measurements. Results There were 85 cases included in the study. The genital angle in males was significantly higher than that in females (51.2 ± 11.3° (n = 36) vs. 18.9 ± 4.1 (n = 49), P < 0.001). The ROC curve revealed the estimated genital angle to have a high degree of accuracy in fetal gender determination (area under the curve ± SE = 1.000 ± 0.001). The best cut‐off for male gender determination was found to be between 27° and 29° (sensitivity, 100%; specificity, 98.0%). There was a high degree of correlation between the two operators (r2 = 0.998; coefficient of variation = 5.4%). Conclusions 3D ultrasound is a highly accurate and reproducible tool for fetal gender assignment prior to 14 weeks of gestation. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.